However, no therapy has shown benefit against hypoxic cell death. A variety of forward genetic screens in C. elegans have implicated protein homeostasis as critical to survival after hypoxia. Using complementary approaches in C. elegans and mouse, we propose to define the mechanisms whereby three distinct but interrelated protein homeostasis pathways control hypoxic injury and adaptation. Our specific aims are: 1) Define the mechanisms whereby the endoplasmic reticulum unfolded protein response (UPR) genes ire-1 and gcn-2 control hypoxic cell death and preconditioning. The UPR gene ire-1 controls hypoxic sensitivity and ire-1 and the UPR gene gcn-2 are absolutely required for delayed hypoxic preconditioning (HP) in C. elegans. A mouse ortholog of ire-1 regulates hypoxic death of mouse hippocampal neurons. Using a combination of C. elegans and mouse genetics, we propose to define the mechanism whereby IRE-1 and GCN-2 regulate hypoxic death and preconditioning. 2) Define the mechanisms whereby p90S6 kinase, mTor, and Srsf1 control hypoxic injury. In both mutagenesis and RNAi screens in C. elegans, knockdown of the expression of multiple translation machinery and regulatory genes have been found to confer hypoxia resistance. RNAi knockdown of the mouse homologs of these genes has identified three genes whose knockdown produces strong protection of mouse neurons from hypoxic injury. These genes function coordinately to regulate the same protein complex. Thus, we propose to examine how these three genes as a group regulate hypoxic injury/adaptation. 3) Determine whether proteostasis is a mechanism whereby the insulin/IGF receptor pathway controls hypoxic death. Mutants in daf-2 are highly resistant to hypoxic injury. Also, knockdown of the daf-2 homolog, insulin receptor related protein [unreadable] Insrr, strongly protects mouse hippocampal neurons from hypoxic death. In C. elegans, multiple investigations have shown that a major mechanism responsible for the increased lifespan and stress resistance of daf-2 is enhancement of protein homeostasis. Thus, we propose to examine whether proteostasis is also a mechanism for the hypoxia resistance of daf-2(rf) and Insrr(rf).